172 HISTORY OF 



have been originally formed by the industry of 

 man. His reasons are, that when a new spring 

 breaks forth, the water does not make itself a new 

 channel, but spreads over the adjacent land. Thus, 

 says he, men are obliged to direct its course, or 

 otherwise nature would never have found one. 

 He enumerates many rivers, that are certainly 

 known, from history, to have been dug by men. 

 He alleges, that no saltwater rivers are found, 

 because men did not want salt water ; and as for 

 salt, that was procurable at a less expense than 

 digging a river for it. However, it costs a spe- 

 culative man but a small expense of thinking to 

 form such an hypothesis. It may, perhaps, en- 

 gross the reader's patience to detain him longer 

 upon it. 



Nevertheless, though philosophy be thus igno- 

 rant as to the production of rivers, yet the laws 

 of their motion, and the nature of their currents, 

 have been very well explained. The Italians 

 have particularly distinguished themselves in this 

 respect, and it is chiefly to them that we are in- 

 debted for the improvement.* 



All rivers have their source either in moun- 

 tains or elevated lakes ; and it is in their descent 

 from these, that they acquire that velocity which 

 maintains their future current. At first their 

 course is generally rapid and headlong ; but it is 

 retarded in its journey by the continual friction 

 against its banks, by the many obstacles it meets 

 to divert its stream, and by the plains generally 



* S, Guglielmini della Natura de Fiumi, passim. 



